As the intraocular pressure (IOP) fluctuates with a diurnal rhythm, there must be some endogenous factors which contribute to the regulation of IOP. Discovery of these natural IOP regulatory factors would lead to a better way of treating glaucoma and ocular hypertension. The specific aims of this study, therefore, include the following: 1. To establish the involvement of melatonergic mechanisms in IOP changes. 2. To correlate diurnal changes of ocular melatonin and those of IOP. 3. To determine the sources of melatonin in eye tissues. 4. To test the hypothesis that the ocular hypotension action of beta-adrenergic blockers is induced through melatonergic mechanisms. 5. To develop pharmacological agents to lower ocular melatonin for glaucoma and ocular hypertension treatment. 6. To study the effects of new drugs on ocular blood flow.